If you're shopping for a mobile spot cooler, you may be wondering what portable air conditioner size you need. Most units will be rated in BTUs — but what the heck does that mean? BTU stands for "British Thermal Unit" and it represents the amount of energy needed to increase the temperature of one pound of water by one degree Fahrenheit.
Generally, the bigger the area you need to cool, the more BTUs you will need.
Take our advice: Don't buy an air conditioner that's too large. An oversized portable air conditioner is actually less effective as opposed to more cooling — and can waste valuable energy at the same time. That means a negative impact on the bottom line of your business.
Because portable air conditioners remove both heat and humidity from the air, an oversized unit may cool the room quickly, but only remove some of the humidity. This will leave your room with a damp, clammy feeling. A properly sized unit will effectively remove humidity as it cools. That means more comfort all around.
Figure out square footage
Size matters. First determine the square footage of the room or area you need to cool.
Determine the square footage of the area to be cooled with a portable air conditioner using the following formulas:
- Square and rectangular rooms: Multiply the length of the area by its width — L x W
- Triangular rooms: Multiply the length of the area by the width and divide it in half — (L x W) / 2
Determine the BTUs needed
Once you have the square footage, refer to the chart below to determine the correct cooling capacity for your portable spot cooler:
| Area to Be Cooled (Square Feet) | Capacity Needed (BTUs per Hour) |
| 100 to 150 | 5,000 |
| 150 to 250 | 6,000 |
| 250 to 300 | 7,000 |
| 300 to 350 | 8,000 |
| 350 to 400 | 9,000 |
| 400 to 450 | 10,000 |
| 450 to 550 | 12,000 |
| 500 to 700 | 14,000 |
| 700 to 1,000 | 18,000 |
Make any adjustments for the following circumstances:
- If the room is heavily shaded, reduce capacity by 10 percent.
- If the room is very sunny, increase capacity by 10 percent.
- If more than two people regularly occupy the room, add 600 BTUs for each additional person.
- If the unit is used in a kitchen, increase capacity by 4,000 BTUs.
- Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction.
Still need advice? Talk to an indoor environmental solutions expert about any special cooling needs you have.
